1. Technical Field
This application is a continuation application of U.S. patent application Ser. No. 13/020,664, filed on Feb. 3, 2011, now U.S. Pat. No. 9,028,476, the entire contents of which are incorporated by reference herein.
2. Description of Related Art
In the treatment of diseases such as cancer, certain types of cancer cells have been found to denature at elevated temperatures (which are slightly lower than temperatures normally injurious to healthy cells.) These types of treatments, known generally as hyperthermia therapy, typically utilize electromagnetic radiation to heat diseased cells to temperatures above 41° C., while maintaining adjacent healthy cells at lower temperatures where irreversible cell destruction will not occur. Other procedures utilizing electromagnetic radiation to heat tissue also include ablation and coagulation of the tissue. Such microwave ablation procedures, e.g., such as those performed for menorrhagia, are typically done to ablate and coagulate the targeted tissue to denature or kill the tissue. Many procedures and types of devices utilizing electromagnetic radiation therapy are known in the art. Such microwave therapy is typically used in the treatment of tissue and organs such as the prostate, heart, liver, lung, kidney, and breast.
Presently, there are several types of microwave probes in use, e.g., monopole, dipole, and helical. A monopole antenna probe consists of a single, elongated microwave conductor exposed at the end of the probe. The probe is typically surrounded by a dielectric sleeve. A dipole antenna consists of a coaxial construction having an inner conductor and an outer conductor with a dielectric junction separating a portion of the inner conductor. The inner conductor may be coupled to a portion corresponding to a first dipole radiating portion, and a portion of the outer conductor may be coupled to a second dipole radiating portion. The dipole radiating portions may be configured such that one radiating portion is located proximally of the dielectric junction, and the other portion is located distally of the dielectric junction. In the monopole and dipole antenna probes, microwave energy generally radiates perpendicularly from the axis of the conductor.
The typical microwave antenna has a long, thin inner conductor that extends along the axis of the probe and is surrounded by a dielectric material and is further surrounded by an outer conductor around the dielectric material such that the outer conductor also extends along the axis of the probe.
In the case of tissue ablation, a high radio frequency electrical current in the range of about 500 MHz to about 10 GHz is applied to a targeted tissue site to create an ablation volume, which may have a particular size and shape. The ablation volume is correlated to antenna design, antenna performance, antenna impedance and tissue impedance. The particular type of tissue ablation procedure may dictate a particular ablation volume in order to achieve a desired surgical outcome. By way of example, and without limitation, a spinal ablation procedure may call for a longer, narrower ablation volume, whereas in a prostate ablation procedure, a more spherical ablation volume may be required.
One particular ablation procedures is a tissue resection procedure. In a tissue resection procedure a clinician first determines that portion of a particular organ, containing unhealthy tissue needs to be resected or removed. A resection line is positioned on the organ, between the unhealthy tissue and the healthy tissue, such that when the tissue along the resection line is ablated, the unhealthy portion may be removed while leaving a sufficient portion of the organ in a viable or functional manor.
One step in a microwave resection or ablation procedure is the step of placing one or more microwave energy delivery device in a portion of target tissue. The placement step is a critical step because proper placement often depends on several factors including the size and shape of the desired ablation region, the type of ablation device (or devices) used, the parameters of the microwave energy signal (i.e., frequency, power, duty-cycle, etc.) and the predicted ablation size that the ablation device may generate.
The placement step becomes even more complicated when the procedure requires a plurality of ablation devices. For example, a resection procedure, which requires the ablation of tissue along a predefined resection line, often requires the placement of a plurality of microwave energy delivery devices along a particular resection line. One particular method of placement includes the insertion of a plurality of tissue penetrating microwave energy delivery devices that are positioned in the target tissue by percutaneous insertion.
In a resection procedure, once the location of the resection line has been determined, the clinician then determines an arrangement of ablation devices that will ablate the tissue along the resection line. This arrangement is typically determined by the predicted ablation region size and shape for the selected ablation device or devices. In most resection procedures a plurality of ablation devices are positioned along the resection line in order to deliver a sufficient amount of energy to achieve complete ablation of the tissue along the resection line.
In one known resection method ablation, the resection is performed by performing a first ablation along a resection line, repositioning the ablation device to a subsequent position along the resection line and performing a subsequent ablation. This step is repeated along the resection line until the entire resection line is ablated. In another resection method, a plurality of ablation devices are inserted along a resection line and the plurality of devices are simultaneously energized (or nearly simultaneously energized) to ablate the tissue along the resection line. While both methods are effective, the first method is time consuming because a plurality of ablations are performed in sequence. The second method requires precise placement of the plurality of devices to insure complete ablation with minimal interaction or interference between adjacent devices.
Regardless of the method used, resection procedures are complicated because the desired ablation region for a typical resection procedure is much different in shape and size than the desired ablation region for a typical ablation procedure. The target tissue in an ablation procedure is typically a tumorous mass that is usually circular, elliptical or oblong. As such, microwave ablation devices have typically been design to generate round, oblong or egg-shaped ablation regions. In contrast to an ablation procedure, a resection procedure typically requires ablation of an elongated region of tissue along the resection line, wherein the length of the ablation region in a resection procedure is typically much greater than the width and/or thickness of the ablation region generated by a typical ablation device.
The difference in shape of the desired ablation region becomes problematic because a clinician typically uses the same ablation device for ablation procedures and resection procedure.